There are Christians that believe they are free from the law, and they think you are trying to take Jesus out of their hearts if you tell them to keep the law. I'm going to make this as simple as possible.
1 Corinthians 5: 7Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us: 8Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Exodus 12:48 And when a stranger shall sojourn with thee, and will keep the passover to the Lord, let all his males be circumcised, and then let him come near and keep it; and he shall be as one that is born in the land: for no uncircumcised person shall eat thereof. 49 One law shall be to him that is homeborn, and unto the stranger that sojourneth among you.
If you want to partake of the body of the Lamb, then you must be circumcised.